We are being asked to calculate the contributions to [H_{3}O^{+}] from each ionization step in H_{2}A.

**H _{2}A**

• can donate two protons (H^{+}) → **diprotic acid**

• two equilibrium equations → two equilibrium constants

• Equilibrium constants (K_{a}) given:

▪ **K _{a1} = 1.0x10^{-4}**

▪ **K _{a2} = 5.0x10^{-5}**

**Construct an ICE Chart for the 1 ^{st} equilibrium reaction:**

Consider a 0.10 M solution of a weak polyprotic acid (H_{2} A) with the possible values of K_{a1 } and K_{a2 } given below. Calculate the contributions to [H_{3}O^{+}] from each ionization step.

K_{a1 } = 1.0x10^{ - 4} ; K_{a2 } = 5.0x10^{ - 5}